1. Field of the Invention
This invention relates to a fixing device which is used in an image forming apparatus such as a copying machine, plotter, laser printer or facsimile machine. The invention further relates to a cleaning blade which scrapes remaining toner from a cleaning roller provided in the fixing device.
2. Discussion of the Background
In Japanese laid open patent 61-193169, a fixing device which fixes toner on a paper sheet has a fixing roller which has a heat source therein, a pressing roller which contacts the fixing roller with pressure, a cleaning roller which is in contact with and cleans the fixing roller and a blade in contact with the cleaning roller and which scrapes attached toner from the cleaning roller.
In the fixing device, the temperature of the surface of the fixing roller is detected by a thermistor which controls the heat source to keep the temperature of the fixing roller surface high enough to soften or melt the toner.
The melted or softened toner is pressed into the fibers of a paper sheet by the fixing roller and pressing roller while the paper sheet is passed through the fixing and pressing roller. In general, a releasing agent is applied on a surface of a fixing roller to reduce the quantity of offset toner.
Toner on the paper sheets is nonetheless transferred onto the fixing roller. The toner transferred onto the fixing roller is negatively (minus) charged. Since the quantity of minus charges on the fixing roller is more than that of the cleaning roller, the toner with negative charge on the fixing roller is transferred onto the cleaning roller by electrostatic adhesion force of the cleaning roller and is scraped by a blade.
Since the blade is in contact on the cleaning roller coated with an insulator, the blade and the cleaning roller are charged by rotation of the roller, whereby the electrostatic adhesion force falls off. Accordingly, it is difficult to sufficiently remove toner from the fixing roller.